CA1086064A - Method and planetary-type lapping machine for lapping a group of workpieces - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A planetary-type lapping machine comprises a station-ary and a rotary lapping discs, and cages arranged therebetween, the cages being essentially planet pinions of a sun-and-planet mechanism and containing the components being machined.
The rotary lapping disc is in a force transmitting connection with the sun gear through a differential gear link.
The differential gear link enables approximately double increase in the angular speed of the lapping disc relative to the angular speed of rotation of the center of said cages about the axis of rotation of said lapping disc.
This relieves the cages from forces applied on the part of the plates being machined.
To maintain parallelism of the lapping discs incor-porated in the drive link of one of the sun gears is a controll-able differential gear link whereby the speed of rotation of the sun gear is varied per cycle.

Description

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The invention relates to machine tools and more parti-cularly to planetary-~ype lapping machines and to methods ~or lapping o~ a group of workpieces on such machines.
The machines o:E the above-mentioned type are designed for machining parallel surfaces of components of hard and fra-gile materials with free abrasive tool, such as -for machining of piezoquartz plates having a thickness of up to 100 mcm, and such machines are provided with a mechanism for kinematic dressing of lapping tools during machining.
~O Known planetary-type lapping machines comprise a lower lapping disc and an upper lapping disc and cages containing com-ponents being machined which are arranged between the discs and driven by a sun gear and a ring gear of a sun-and-planet gear which are rotated on vertical shafts coaxial with the stationary lower lapping disc and rotary upper lapping discs (lapping tools).
In such machines, circumferential speeds of the cage center re-lative to the surface of the lapping discs are about equal and opposite, and there is provided a mechanism fox rotating the upper lapping disc which is driven by one of the links of the sun-and-planet year of the machine (cf. USSR Inventor's Certifi~
c~te No. 1~92911).
Alongside with the advantages of such construction of the machine consisting in that there is provided a stationary base surface (lower lapping disc), the cage is relieved because force~ of friction o the plate over the surface of the lapping discs are directed at an obtuse angle, and there is a possibility of movement of the workpieces being machined along spiral paths, there are also a number of disadvantages, such as discussed here-.... .;.;, .
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The plates being machined can only move, over the sur-faces of the lapping tools, along "circular" paths which results in an increased wear of teeth due to a large number of plates being machined in the cage and high circum~erential speed o~ the cage teeth relative to the teeth of the sun and ring gears o~
the sun-and-planet gear. The cage size is equal to the size of the sun gear so that it is impossible to make the machine having narrow lapping tools and smaller cages which is especially im-portant in machining thin plates.
It is known that the smaller the cage, the`lower thenumber of plates loaded therein, hence the lower the resultant ~orce (composed of all frietion forces acting on each plate) applied to the cage. With the cage and sun gear sizes being equal, reduetion of the cage dimensions results in reduced dimen-sions of the lapping discs and lower number of concurrently ma-ehined plates, hence the productivity decreases.
Where the ec~ality of sizes of the cage and sun gear i~ not required, the machine with smaller eages and larger num-ber of them may be made. Therefore, with the same outside dimen-~ions of the lapping dises, the number of concurrently machined plates remains the same since a larger number of smaller cages axe loaded in the maehine.
Known maehines, sueh as the lapping machine AL-2 manu-- Eaetured by Peter Wolters (West Germany) provide for kinematic clre~sing by eoneurrently reversing the lower and upper lapping digCS, it is, however, impossible to machine thin pla-tes to high aeeuracy using such machine, since both lapping discs are rotat-.. `' "

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able. The reverse of the upper lapping disc with the stationary lower lappiny disc would not brin~ about a desired r~sult be-cause tha cages could not be unloaded, hence minimum thickness would be unobtainable.
It is an object of the invention to provide a plane-tary-type plane lapping machine which enables machining of plates (components) of minimum thickness, such as of 60-80 mcm with thickness differentials within the range from 0.25 to 0.5 mcm.
Another object of -the invention is to provide a plane-tary-type plane lapping machine which ensures uniform wear over the entire working sur~ace o~ the lapping tool during machining.
Further object of the invention is to provide a plane-tary-type plane lapping tool which provides for reduction or complete elimination of the action of components being machined on the cage.
Another object of the invention is to provide a plane-tary--type plane lapping machine which enables the control of directive wear of the working surfaces of the lapping tools dur-ing machining.
Still anothar object of the invention is to provide a planetary-type plana lapping tool in which tha above-mentioned advantages are obtained due to relatively simple and inexpensive modi~ications o~ axisting planetary-type lapping machines.
It is also an object of the invention to provide a planetary-type plane lapping machine which enables substantial lowering oE requirements imposed on the cage material.
Further object o~ the invention is to provide a plane--tary-type plane lapping machine in which ~orce application on the ; part of the cage teeth to the sun gears teeth is eliminated.

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And ~inally, i~ is an objec-t o~ the inventlon to provide a planetary-type plane lapping machine in which the service life of gears is prolonged by more than 100 times.
For the accomplishment of the above objects, according to the invention, there is contemplated a method for lappiny a group of workpieces in cages on planetary-type plane lapping machines in which the components being machined are arranged be-tween rotary lapping discs and a stationary lapping disc. The method is characterized in that the rotary lapping disc is driven at approximately doubled angular speed compared to the angular .

speed of rotation of the cage cen-ters about the axis of rotation of the lapping disc thereby relieving the cages from the action of the components being machined.
There is also contemplated a planetary-type plane lapp-ing machine for carrying out the above-described method compris-ing a stationary lapping disc and rotary lapping discs, the com-ponents being machined being arranged in cages between the discs, the cages being formed as planet pinions of a sun-and-planet gear driven by a sun gear and a ring gear, characterized in that there is provided a differential gear link inserted between the sun ~ear and the rotary lapping disc for making the gear ratio between the sun gear and the lapping disc of about 1:2.
This construction enables the elimination of force transmitting action of the components being machined on the cage ~u~ to opposite direction of friction forces developing during mach.in.ing between the components and working surfaces of lapping tools at the opposite sides of the plate being machined.
In accordance with one embodiment of the invention, there is provided a plane lapping machine characterized in that the differential gear link providing for the above-mentioned . . . . .. .

angular speed ratio comprises a cross-piece rigidly connected to the sun gear, the cross-piece supporting loosely mounted inter-meshing pinions meshing with a pair of other pinions coaxial with the sun gear, one pinion being fixed and the other being in a drivlng connection with the rotary lapping disc by means of a Carrler.
This construction provides the most preferable means for elimination of force transmitting action of the components being machined on the cage according to the first embodiment of the invention. Such technical solution permits the use of an independent drive of the upper lapping tool to be dispensed with due to the provision of the differential mechanism for driving the upper lapping disc directly from the central shaft.
And finally, according to still another modification o~ the invention, there is provided a plane lapping machine characterized in that the force transmitting connection of the drive of the sun gear of the sun~and-planet lapping gear in-cludes a differential mechanism for controlling the directive wear of the working surfaces of the lapping discs which comprises a reversible electric motor, a reduc-tion gear, and intermediate gear, two sun gears, a carrier and planet pinions.
This construct.ion enables the elimination of force ~ransmitting action of the components being machined on the cage as in the case of the first embodiment of the inven-tion and also enables kinematic dressing of lapping tools during machining by var~ing the kinematic performance~
-~ In accordance with one aspect of the present invention there i9 provided a planetary-type lapping machine comprising a : -5-, :, .
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stationary lapping disc, a rotary lapping disc, cages disposed between said stationary and rotary discs, as well as sockets to accommodate workpieces being machined, and sun and ring gears, said cages forming planetary gear trains meshing with and driven by the sun and ring gears, the sun gear being engaged with the rotary lapping disc via a gear train which drives -the rotary lapping disc at approximately double the angular speed of the centers of said cages about the axis of rotation of said lapping disc, thereby relieving the cages from the application of forces on the part of the workpieces being machined.
The invention will now be described in details with reference to the accompanying drawings, in which:
Figure 1 (a,b,c) diagrammatically shows the machining of work pieces on the plane lapping machine according to the invention, Figure 2 shows a first embodiment of the invention with the drive of the upper lapping disc directly from the cen-~ txal shaft, Figure 3 shows a second embodiment o-E the lapping machine with the differential drive of the upper lapping disc.
Known planetary lapping machines comprise an upper and a lower lapping tools and cages arranged therebetween and driven by sun and ring gears rotating on vertical rotary shafts.
Plates being machined are placed in sockets oE the cages and lapped over the plane surfaces o~ the lapping tools.
The existing types of plane lapping machines enable machining.of plane parallel surfaces of components of various materials to high accuracy and at high performance. Alongside ,: ' ' : . ' : ~

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with the above, these rnachines offer restricted opportunities in machining thin plates, and to obtain high accuracy of components being machined, the lapping tools should be removed from the machine, and the working surface of the lapping tools should be dressed~
In addition, high loads on the cages at the points of contact with -the components being machined and at the points of contact of teeth with the sun gears result in a rapid wear of the cages and crowns of the sun gears.
It is obvious that the obtainable thickness of the plates to be simultaneously machined on both sides depends to a great extent on the cage strength. The cage is used for placing and holding the components being machined. The cage takes-up *orces applied on the part of the sun gears to the gearing points, as well as forces of useful resistance on the part of the upper and lower lapping tools which are applied to the cage through the components being machined.
The experience of lapping of plates with a thickness exceeding 0.5 mm offers a large variety of materials for the ~0 manu~acture of cages~ However, in machining plates of a thic~-ness smaller than 0.5 mm using the same materials, the load on the cage is to ~e lowered.
This is practically possible by selecting such kinema-kic performance for the actuating mechanism of the lapping machine wi-th which the resultant force (~ P) during machining has a mini-mal and sufficiently steady value within the cycle.
In machining plates on a lapping machine having station-ary lapping tools, directions f the resistance ~orces (P14 and P24) ~~ ' ', .
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coincide slnce the plate center moves along the paths of similar eonfigurations over the sur~ace o~ lapping tools.
Figure 1 shows:
(a) a diagram showing the direction of relative speeds and resistance forces in machining plates between stationary lapping tools 1 and 2, (b) the same, with machining of plates between lapping tools 3,4 rotating in opposite direetions;
(e) the same, with maehining o~ plates between a stationary lower and rotary upper lapping tools 5,6.
The first system ~or machining plates 7 provides ~or high aeeuracy of machined plates which is due to the provision of -the stationary support base formed by the lower lapping tool

2. However, when using this system (Flgure la), a cage 8 takes-up maximum load sinee useful resistance forces are applied in the same direetion (P=Pl4~p24).
In maehining plates on a lapping tool having the oppo-sitely rotating lapping tools 3,~ (Figure lb), resistance forces Pl~ and P2~ are opposite. ~ eage 9 is loaded with a low force whieh is equal to the differenee in the resistanee forees 5 P=Pl~-P2~. This system provides for maehining of thin plates 7, however, the absenee of stationary support base hampers high-aeeuraey maehining of the plates. 1, In maehining plates on the lapping maehine with thesta-tionary lower lapping tool 6 (Figure lc) and the rotary upper lapping tool 5, an additional eondition should be complied with:
~p~ds of movement of the eomponent 7 being maehined relative to the upper and lower lapping tools 5,6, respeetively, should be ~; 8 ` ' ;: '. ' ' ~, " ' ' ~ ~, ' ' '' , "' ' ' ' ' ' :'~ ' ' ; ' ' ' ,':. ;
, 3L6~16~64 about equal~ This is necessary to obtain the same rate of re-moval of the allowance from both sides of the plate.
~ herefore, the construction of the machine, in which the lower lapping tool 6 is stationary, the center of a cage 10 moves at an angular speed ~3, and the upper lapping tool rotates at an angular speed ~1=2~3, provides for machining of thin plates due to the fact that the cages are relieved from resist-ance forces on -the part of the plates being machined and ensures high accuracy of machining due to the maintenance of a station-ary support base since the lower lapping tool 6 is stationary.
In practice, this system of machining may be carriedout if the selection of kinematic performance of a planetary type plane lapping machine provides for approximate equality of angular speeds of the sun gears ~5=~6' the mandatory condition being ~ 3. In such case, the angular speed of the upper lapp-ing disc (lapping tool) should be by about two times higher than the angular speed of the sun gear.
This construction of the machine ensures the movement of the center of plates being machined along spiral paths over the working surfaces of the lower and upper lapping tools, In this case, the angle between vectors of circumferential speeds or xesistance forces on the side of the upper and lower lapping tools only slightly differs from 180 at any point of the lapping tool surface. i Therefore, in one embodimen-t of the invention, the lapping machine comprises an upper lapping disc 11 (Fig. 2) and a lower lapping disc 12, and cages 13 arranged between them.
Plates 1~ being machined are placed in sockets o~ the cages 13.

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. -'' ~-' ' -The cages 13 mesh with teeth of a sun gear 15 and a ring gear 16 a sun-and-planet gear. The upper lapping disc 11 has stops 17 engaging pins 18 of a double-speed multiplier. The double-speed multiplier comprises a carrier 19, a spherical bearing 20, a cross-piece 21 rigidly fitted on a central shaf-t 22, a support gear 23, planet pinions 24 and a ring gear 25 of the multiplier.
The upper lapping disc 11 is journalled in support rollers 26.
The machine also comprises an electric motor 27, a reduction gear 28 and an intermediate shaft 29.
Upon energization of the electric motor 27, rotary motion is transmitted, via the reduction gear 28 and intermediate shaft 29, to the central shaft 22 and ring gear 16 of the sun-and-planet gear. The sun gear 15 of the sun-and-planet gear and the cross-piece 21 are rigidly secured to the central shaft 22 ~o that they are driven at the same angular speed. The planet pinions 24 fixed to the carrier 19 roll over the .support gear 23 to drive ring gear 25 of the double-speed multiplier at an angu-lar speed which is twice the speed of the sun gear 15 of the sun-and-planet gear.
In accordance with another embodiment of the invention, the lapping machine comprises an upper lapping disc 31 (Figure 3) and a lower lapping disc 32, and cages 33 arranged between the discs~ Plates 34 being machined are placed in soc~ets of the ~ag~s ~3. The cages mesh with teeth of a sun gear 35 a ring ar 36 of a sun-and-planet lapping gear. The upper lapping disc ~as s-top~ 37 engages pins 3~ of a sun-and-planet gear driving the upper lapping disc comprising a carrier 39, a spherical bearing 40, a cross-piece 41 rigidly fitted on a central shaft 42, a ,~

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support gear 43, planet pinions 44 and a ring gear 45 of a double-speed multiplier. The upper lapping disc is journalled in rollers ~6. In addition, -there are provided a distribution shaft 47 and an electric motor 48.
The machine also comprises a correction mechanism which consists of a reversible electric motor 49, a worm gearing 50 having a self-braking worm couple, intermediate shafts 51 and 52, a carrier 53 and an internal gear 54.
The system according to the invention involves the 10 operation of the machine in three different modes:
A- conventional mode, s- correction of the discs with depression towards the center, C- correction of the discs with depression towards the periphery.
During operation in the mode A, the motor 48 is put on, and the correction motor 49 is put off. The worm gearing 50 brakes the gear 54 of the sun-and-planet correction gear. Motion from the motor 48 is transmitted, via the intermediate shaft 52, carrier 53, intermediate shafts 42 and 47, to the sun geàr 35 and ring gear 36 of the sun-and-planet lapping gear. The upper lapp-~) in~ disc 31 is driver~, via the sun-and-planet drive gear including -the members 41, 44, 39 and stops 37. With the time, the lapping disc is worn from the center towards the periphery. In such case, ~he motor ~9 is put on to rotate in a selected direction to in-cre~se or decrease the rotational speed of the external gear 36 and provide for a change of the path so that the lapping discs 31 and 32 are dressed during machining of the plates 34.
Thus, in order to the obtain steady accuracy of the plates being machined in the lapping machine according to the ~, . . .

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invention, there is provided, in the force transmittir,g system of the machine, which connects the sun gear to the ring gear, a second sun-and-planet gear driven by the worm gearing incorporat-ing a self-braking worm couple and an individual reversible electric motor which is necessary for correction of the worn working surface of the lapping tools. The worn surface is con-vex or concave.
Generally, the machine operates with the correction electric motor off. In a certain time, when a directive wear of the lapping tools appears, the correction electric motor is put on, and the rotational direction of the motor depends on the shape of the worn surface (convex or concave). The mechanism according to the invention permits the plane parallelism of the lapping disc to be maintained during a long time.
Alongside with the relief of the cages from force application on the part of the plates being machined, this system prolongs the life of teeth, cages and sun gears for two reasons.
First, alongside with the reduction of the resistance forces, the forces in the gearing are also lowered. Second, with l~5-~6' the relative sliding speed of the teeth is reduced.
The above-mentioned advantages of the machine according -to the invention may be summarized as follows: tl) the cages are relieved from forces applied on the part of the plates being machined, (2) service life of the carriages and sun gear teeth is pxolonged, (3) the shape of the worn surface o~ the lapping disc~ is stabilized, and these advantages may be achieved in lapping machined independently on one another so as to obtain savings in operation of the machines, the above principles being ., , -.. . .

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theoretically elaborated and tested. How~ver, it is noted tha-t it is the comprehensive incorporation o:E all technical solutions described above in a single machine ~hat enables the production of a plane lapping machine coping with stringen production requirements of stability, accuracy and productivity in machin-ing thin plates.

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Claims (3)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:-

1. A planetary-type lapping machine comprising a station-ary lapping disc, a rotary lapping disc, cages disposed between said stationary and rotary discs, as well as sockets to accommo-date workpieces being machined, and sun and ring gears, said cages forming planetary gear trains meshing with and driven by the sun and ring gears, the sun gear being engaged with the rotary lapping disc via a gear train which drives the rotary lapping disc at approximately double the angular speed of the centers of said cages about the axis of rotation of said lapping disc, thereby relieving the cages from the application of forces on the part of the workpieces being machined.

2. A plane lapping machine according to claim 1, wherein said gear train comprises a cross-piece rigidly connected to the sun gear, a transverse bar supporting loosely mounted inter-meshing pinions adapted to mesh with a second pair of pinions arranged co-axially with the sun gear, one of said second pinions being rigidly fixed, and the other pinion being in a driving connection with the rotary lapping disc by means of a carrier.

3. A plane lapping machine according to claim 1, wherein the gear train comprises a differential gear to control the direction of wear of the working surfaces of the lapping discs, said differential gear comprising a reversible electric motor, a reduction gear, an intermediate gear, two sun gears, a plura-lity of carriers and planetary pinions.